Whilst being interviewed by the police family liaison officer, Karen (played by Gemma Whelan) got up and started dancing to the detective’s ring tone.
Despite the fact her daughter, Shannon, had been missing for several days, Karen acted like she didn't have a care in the world.
She later sat down after being told to so by one of her friends, before adding: “I just love that ring tone.”
Those watching at home could not believe Karen, who was later revealed to have been behind the fake kidnapping plot, had really behaved in such a way.
“Did Karen Matthews actually get up and dance to the ring tone #TheMoorside,” one social media user asked.
The Moorside viewers were shocked after watching Karen Matthews dance to a police officer's phone
The Moorside: The scene was based on a true event
“Surely Karen didn't get up and start dancing to the DC's ringtone?? #TheMoorside,” another added.
Someone else said: “Can't believe Karen Matthews started dancing to the police woman's 'brown eyed girl' ringtone #themoorside.”
A fourth remarked: “F***ing screaming @ Karen Matthews dancing to brown eyed girl #TheMoorside.”
However, the scene was in fact based on the real life testimony of one of the police officers involved in the case.
The Moorside: Former detective Christine Freeman said she knew at that point something was not right
Moorside: The real story
Tue, February 7, 2017
Moorside: The new BBC drama follows Sheridan Smith, as Julie Bushby, in the search for missing school girl Shannon Matthews. Here's the real story behind the programme.
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Christine Freeman, the detective charged with looking into the disappearance of the nine-year-old, told the Daily Telegraph that this was the moment she realised something was not right.
She recalled: “When I got to the house Karen and her boyfriend, Craig Meehan, were playing on an X-Box. Karen hardly looked up.
“After a few minutes my phone rang. I had a pop song as my ringtone and Karen got up and started dancing to it. I remember thinking ‘this is really odd’."
The Moorside continues next Tuesday at 9pm on BBC One.